Switching mode power supply with a voltage clamping circuit

ABSTRACT

The anti-windup circuit generally has a voltage clamping device in series with a current limiting device operatively connectable to the output current path of a feedback compensator; the feedback compensator being part of a switch-mode power supply (SMPS) having an input voltage source and a load and generating constrained control values required to generate control on-off actions for tight power regulation. The inclusion of the disclosed anti-windup circuit in an SMPS may lead to hardware based overvoltage protection, reduced overall size and faster response to load changes.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of co-pending U.S. patentapplication Ser. No. 15/249,623, filed Aug. 29, 2016, all of which ishereby incorporated by reference in its entirety.

FIELD

Example embodiments generally relate to the field of switch-mode powersupplies, and more particularly to the field of analog and mixed-signalcontrol of isolated and non-isolated switch-mode power supplies and moreparticularly to the field of overvoltage protection.

BACKGROUND

Switch-mode power supplies (SMPSs) are important power managementcomponents in modern electronic devices. They provide, among otherthings, tightly regulated power to multiple sub-systems during alloperating conditions. In order to achieve tight power regulation,conventionally one or more affordable and compact analog feedbackcontrol loops and multiple bulk reactive energy storage elements arerequired. The feedback control loops direct the energy flow between theSMPS input and output ports as quickly as possible, while the expensiveand bulky energy storage elements consume/provide the difference betweenthe input and output energy.

In order to ensure tight power regulation during steady-state, thefeedback loop compensators utilize one or more integrators. However,during periods of control saturation, such as when the compensatorgenerates negative control values, the compensator integrator componentscan suffer from wind-up phenomenon, causing control action delays andincreased output voltage deviations. This results in an increase of thebulk reactive energy storage requirements, contributing to increasedSMPS volume and cost. By constraining the duration and magnitude ofwind-up, one can reduce the power loss, size and cost of switch-modepower supplies.

Additional difficulties with existing systems may be appreciated in viewof the instant disclosure.

SUMMARY

In an example embodiment, there is provided an anti-windup circuit foruse with a switching mode power supply involving a voltage clampingdevice and, in an example embodiment, a series current limiting deviceconnected in parallel with the output current path of the feedbackcompensator.

The voltage clamping device may be in the form of a Zener diode,controlled Zener device (such as TL431, or others), transient voltagesuppression (TVS) diode, voltage-dependent resistor (VDR), avalanchediode or similar device. By clamping the voltage of the output currentpath of the feedback compensator, a programmable restriction on thefeedback current value, that is a minimum control value, may be imposed.In such a way, the embodiment minimizes the charging of the feedbackcompensator integrator during non-controllable states of operation,mitigating the wind-up phenomenon. The embodiment may also provideoutput voltage clamping (overvoltage protection) during periods of largevoltage difference between the reference and instantaneous outputvoltage values, e.g. heavy-to-light load transients. In such a way, thefeedback control delays may be minimized during transient states and themaximum positive difference between the output voltage and the referencevoltage value may be minimized allowing for the reduction of the bulkreactive component storage requirements.

In an example embodiment, the series current limiting device may beprovided in the form of a resistor, parasitic resistance, thermistor, oractive current limiter. By limiting the current through the voltageclamping device, the maximum power dissipation of the voltage clampingdevice may be programmed. Furthermore, by limiting the current throughthe voltage clamping device the discharge rate of the SMPS output portreactive components during over-voltage conditions, which typicallyoccur during heavy-to-light load transitions, may be adjusted.

In accordance with one aspect, there is provided a method for selectingthe voltage clamping value, the method comprising: forcing the SMPS tooperate near the controllability and non-controllability boundary, andmeasuring/calculating the feedback compensator output current pathvoltage.

According to an aspect, there is provided a switching mode power supplyhaving a converter; a voltage input for the converter; a voltage outputfrom the converter and configured to electrically couple to a load; afeedback compensator controlling the converter in response to detectingthe voltage output; and an anti-windup circuit comprising a voltageclamping circuit connected in parallel with the feedback compensator.According to some aspects, the anti-windup circuit may minimizedeviation of the output voltage during light-to-heavy transients.

The feedback compensator may generate a control signal for controllingthe converter. In some aspects, the control signal may provide input toa pulse width modulator where the pulse width modulator providingswitching input to the converter. The feedback compensator may generatethe control signal using a comparison between the detected voltageoutput and a reference voltage to reduce deviation of the outputvoltage. The feedback compensator may compriseproportional-integral-derivative (PID) control. In some aspects, thefeedback compensator may be an analog feedback compensator.

According to some aspects, the voltage clamping device may providetransient overvoltage protection. The voltage clamping circuit may beselected from at least one of a Zener diode, a shunt regulator, anactive Zener device, a transient voltage suppression (TVS) diode, avoltage-dependent resistor (VDR), an avalanche diode, and/or anycombination thereof.

In accordance with another aspect, the switching mode power supply mayfurther comprise a comparator that may generate a negative controlsignal when the output voltage exceeds the reference voltage. Theanti-windup circuit may reduce negative control signals from thecomparator.

According to yet another aspect, the feedback compensator may generatethe control signal according to at least one of discontinuous-currentmodulation (DCM), continuous-current modulation (CCM), pulse-frequencymodulation (PFM), or quasi-resonant frequency (QR) operation.

According to other aspects, the anti-windup circuit may further comprisea current limiting circuit connected in series with the voltage clampingcircuit. The current limiting circuit may be one or more of afield-effect transistor, a resistor, a thermistor, an active currentlimiter, and/or any combination thereof.

Some aspects may further have the feedback compensator isolating thevoltage output from the control of the converter and the feedbackcompensator may be isolated using an opto-coupler.

According to another aspect, the switching mode power supply may beconfigured to accept either an alternating current or direct current asthe voltage input. The converter may be a flyback converter.

According to another aspect, there is provided a method for selecting aclamping voltage for a voltage clamping circuit connected in parallelwith a feedback compensator of a switching mode power supply. The methodmay operate the switching mode power supply, without the voltageclamping circuit, at a controllability and a non-controllabilityboundary; determine potential connection points for the voltage clampingcircuit; calculate or measure a maximum differential analog voltage ateach of the potential connection points; and select potential connectionpoint for the voltage clamping circuit that has a minimally largerclamping voltage.

The method may additionally vary at least one transient operatingcondition of the switching mode power supply. The method may alsooptimize the voltage clamping circuit to reduce the feedback compensatorwind-up and minimize an output voltage deviation during a heavy-to-lightload transient operating condition and/or optimize the voltage clampingcircuit to minimize the output voltage settling time during at least onetransient operating condition.

According to yet another aspect there is provided a method of convertinga voltage input into a voltage output. The method may receive thevoltage input at a converter; convert the voltage input into the voltageoutput using the converter; connect the voltage output to a load; detectthe voltage output across the load; control the converter in response tothe detected voltage output using a compensator; and reduce the voltageoutput deviation using an anti-windup circuit comprising a voltageclamping circuit connected in parallel with the feedback compensator.

Many further features and combinations thereof may appear to thoseskilled in the art following a reading of the instant disclosure.

BRIEF DESCRIPTION OF THE FIGURES

One or more embodiments will now be described, by way of example only,with reference to the attached Figures, wherein:

FIG. 1 is a schematic diagram of an example of a power supply, includingan input voltage source, a SMPS, and an anti-windup feedback loop;

FIG. 2 is a schematic diagram of an example of a flyback converter forconverting alternating current (AC) to direct current (DC);

FIG. 3A is a schematic diagram of an example of the anti-windupnon-isolated analog voltage mode type 2 compensator based on TL431-typeshunt regulator of FIG. 1;

FIG. 3B is a schematic diagram of an example of the anti-windup isolatedanalog voltage mode type 2 compensator based on TL431-type shuntregulator and an opto-coupler of FIG. 2;

FIG. 4 is a schematic diagram of an example of the anti-windup circuitwith current limiting;

FIG. 5 is a graph of an exemplary curve showing the evolution of anoutput voltage, load current and control signal before, during and afteran integrator wind-up condition of a flyback converter of FIG. 2;

FIG. 6 is a graph showing the output voltage, feedback compensatoroutput voltage and feedback compensator output currents as a function oftime for a simulated flyback converter before, during and after awind-up occurrence;

FIG. 7 is a graph showing the evolution of the output voltage, feedbackcompensator output voltage, feedback compensator output currents andanti-windup circuit current as a function of time for a simulatedflyback converter with the anti-windup circuit during the same operatingconditions as in FIG. 6;

FIG. 8 is a graph showing the evolution of the output voltage, feedbackcompensator output voltage, feedback compensator output currents andanti-windup circuit current as a function of time for a simulatedflyback converter with the current limited anti-windup circuit duringthe same operating conditions as in FIG. 6; and

FIG. 9 is a flowchart demonstrating a method for selecting a clampingvoltage for a voltage clamping circuit of a switching mode power supply.

These drawings depict exemplary embodiments for illustrative purposes,and variations, alternative configurations, alternative components andmodifications may be made to these exemplary figures.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 shows an example of a power supply 100, in accordance with anembodiment. As depicted, the power supply 100 may have a voltage source110 connected to the primary side port of a switching-mode power supply(SMPS) 120 with an input voltage V. The input voltage V_(in) may beprovided either as an alternating current (AC) or as a direct current(DC). The secondary side port of SMPS 120 is, in turn, connected to anoutput load 130 providing an output voltage V_(out). The output voltageV_(out) may be sensed and compared to a reference voltage V_(ref) by asubtractor 140. The voltage difference V_(e) is then processed by acompensator 150, which includes the embodied anti-windup circuit 160, inorder to calculate a control signal V_(c). The compensator 150 maycomprise proportional, integral, or derivative control using a PI or PIDcontroller. The control signal V_(c) is passed to, in this exampleembodiment, a pulse-width modulator (PWM) 170 which generates anequivalent SMPS 120 switch on-off control actions. The control signalV_(c) may be for discontinuous-current modulation (DCM),continuous-current modulation (CCM), pulse-frequency modulation (PFM),and/or quasi-resonant frequency (QR) operation.

FIG. 2 is another example of the power supply 100 for convertingalternating current (AC) to direct current (DC). As shown, the flybackconverter 121 has the voltage source 110 which is adapted, in thisexample, to provide AC voltage through an initial forward-biased diodeD₁. The power supply 100 may have an input capacitor C_(in) across theinput to the flyback converter 121. The flyback converter 121 comprisesa transformer T₁ in series with a transistor Q₁, which is switched usingthe output from the PWM circuit 170. The output of the transformer T₁passes through a second forward-biased diode D₂. An output capacitorC_(out) further smoothes the output voltage V_(out). The load currenti_(load) produces the output voltage V_(out). This specific embodimenthas an isolated anti-windup circuit 160 equipped feedback compensator151 that controls the PWM circuit 170.

Turning now to FIG. 3A, an example of the anti-windup circuit 160 withinthe compensator 150. In this example, the compensator 150 may be anon-isolated type 2 compensator 150 based on a TL431 shunt regulator(e.g. Precision Programmable Reference) produced by Texas Instruments.The embodiment is composed of a Zener diode voltage clamping device Z₁and a series resistive current limiting device R_(z), placed in parallelwith the output of the compensator output current path, i_(fb1)(t). Theoutput current i_(fb1)(t) is mirrored through one or more currentmirrors such as in this example, current mirror CM₁ and current mirrorCM₂ to produce the control voltage V_(c)(t) that controls the PWMcircuit 170.

FIG. 3B is another example of the anti-windup circuit 160 within thecompensator 151. In this example, the compensator 151 may be an isolatedtype 2 compensator 151 based on a TL431 shunt regulator and opto-couplerOC₁. The circuit is composed of a Zener diode voltage clamping device Z₁and a series resistive current limiting device R_(z), placed in parallelwith the output of the compensator output current path, _(fb1). Theoutput current path i_(fb1) passes through the opto-coupler OC₁ and maybe mirrored though a current mirror CM₁ to produce the control voltageV_(c)(t) that controls the PWM circuit 170.

FIG. 4 is another example of the anti-windup circuit 160 with a seriescurrent limiting device Q₁ which is adapted, in this example, to alsoclamp the current below a programmable maximum value. The anti-windupcircuit 160 comprises a TL431 voltage clamping device and a feedbackbased P-Type Field-Effect Transistor (FET) Q₁ or resistive currentlimiting device. The TL431 voltage clamping device engages when thecompensator output current path voltage V₄(t) is greater than aprogrammable reference voltage ˜(1+R_(f1)/R_(f2))*V_(ref)(t). Duringthis period the i_(z)(t) current is adjusted up to a maximum currentvalue equal to V_(gs)(t)/R_(cs).

The principle of operation of the embodiments shown in FIG. 3A, FIG. 3Band FIG. 4 may be explained by first analyzing the operation of theflyback converter 121 during integrator windup. FIG. 5 illustrates theoutput voltage V_(out), output load current i_(load) and feedbackcompensator output voltage V_(c) and integrator voltage waveformsoccurring during integrator windup conditions, caused in this example bya heavy-to-light load transient. A sufficiently large positivedifference between the output voltage V_(out) and the reference outputvoltage V_(ref) eventually causes the feedback compensator 150 controlvoltage V_(c) to reach zero. This zero point coincides with thecontrollability and non-controllability boundary point of the flybackconverter 121, past which the feedback compensator integrator 150experiences windup. Specifically, the circuit attempts to generate anegative control voltage V_(c); however, due to the limitations of theflyback converter 121, a unidirectional power transfer SMPS 120, the PWM170 is unable to generate an equivalent control action. As a result,without an anti-windup circuit the feedback compensator 150 (integrator)component increases until a negative voltage difference between theoutput voltage V_(out) and reference output voltage V_(ref) occurs. Atthis point, the feedback compensator 150 control voltage V_(c) remainsat zero until the integrator component voltage winds-down, causing asignificant control action delay t_(delay). The result of the time delayt_(delay) is a large output voltage V_(out) deviation ΔV_(windup),increasing the reactive component energy storage requirements.

The embodiments describe herein eliminate or significantly reduce thewindup phenomenon by limiting the compensator 150/151 operation to acontrollability region, specifically by limiting the compensator 150/151from generating a negative control voltage V_(c)(t) or equivalently anunbounded compensator output current i_(fb1)(t) and/or i_(fb2)(t). Thismay be achieved with a voltage clamping device, such as a TL431, placedin parallel with the output current path of the compensator 150/151.

Other examples may contain a protective current limiting device thatlimits (resistive element in FIG. 3A and FIG. 3B) or clamps (currentsensor R_(cs) and P-Type FET Q₁ in FIG. 4) the current through thevoltage clamping device TL431.

FIG. 6 shows the output voltage V_(out), type 2 feedback compensatoroutput current paths i_(fb1)(t) and i_(fb2)(t), and the compensatoroutput current path voltage V₄(t) graphs during a simulated flybackconverter 121 integrator wind-up condition. FIG. 7 illustrates similargraphs for the anti-windup circuit 160 with the type 2 compensator 151as shown in FIG. 3B. As can be seen, the type 2 compensator 151 enablessix times reduction of the output voltage deviation (allowing for anequivalent reduction of the output reactive component size) and greaterthan 40% reduction of the settling time. Similar graphs are alsoillustrated in FIG. 8 for the when the anti-windup circuit 160 hascurrent clamping, as shown in FIG. 4, being added to the type 2compensator 151. The current clamping example enables a similarreduction of the output voltage V_(out), settling time and maximumcurrent.

Turning now to FIG. 9, a method for selecting a clamping voltage for avoltage clamping circuit is shown. The method 900 starts at step 902 byidentifying potential connection points for the voltage clamping device(e.g. in parallel with the output current path of the feedbackcompensator). The SMPS may be operated near a controllability (ornon-controllability) boundary (step 904), such as, for example, at aminimum control signal. The differential voltage may be measured (or inthe case of a simulation, calculated) at the potential connection pointsfor the voltage clamping device (step 906). The voltage clamping devicemay be selected with a marginally larger clamping voltage than measured(or calculated) at step 908. The voltage clamping device may be placedin parallel with the selected connection point (step 910).

An example embodiment is a method for selecting the voltage clampingvalue, the method including forcing the SMPS to operate near thecontrollability and non-controllability boundary, andmeasuring/calculating the feedback compensator output current pathvoltage.

In an example embodiment, the method is for selecting a clamping voltagefor a voltage clamping circuit connected in parallel with the outputcurrent path of the feedback compensator of a switching mode powersupply. The method includes: operating the switching mode power supply,without the voltage clamping circuit, at a controllability and anon-controllability boundary; identifying potential connection pointsfor the voltage clamping circuit which are in parallel with thecompensator output current path (e.g. as shown in FIGS. 3A and 3B);calculating or measuring a maximum differential analog voltage at eachof the potential connection points; and selecting the voltage clampingcircuit that has a minimally larger clamping voltage than measuredmaximum differential analog voltage at each potential connection point.

Although particular current mirrors are demonstrated herein, other typesof current mirrors may be substituted without affecting the operation ofthe circuits.

Although the voltage clamping device is shown with particular examples,other voltage clamping devices may be a Zener diode, a shunt regulator,an active Zener device (such as TL431 or others), a transient voltagesuppression (TVS) diode, a voltage-dependent resistor (VDR), and/or anavalanche diode or similar device.

Although the current limiting device is described herein according toparticular examples, other current limiting device such as a resistor(parasitic or added), a thermistor, and/or an active current limiter maybe used.

Although the feedback compensator described herein implementsproportional-integral-derivative (PID) control in an example embodiment,other feedback control systems may be used, which contain an integraltype control action (e.g. proportional-integral (PI)) in other exampleembodiments.

As can be understood, the examples described above and illustrated areintended to be exemplary only. For instance, as may be readilyunderstood by one skilled in the art, other embodiments of theanti-windup circuit 160 may be constructed with several differentvoltage clamping and current limiting devices, such as avalanche diodesand voltage-dependent resistors for the former and thermistors orBJT/FET based active current limiters for the latter.

In another example embodiment, an anti-windup kit may be provided forelectrical attachment to the power supply. The kit may comprise afeedback compensator for attachment to the voltage output of the powersupply, an anti-windup circuit comprising a voltage clamping circuitconnected in parallel with the feedback compensator. In an exampleembodiment, the kit may include a plurality of different voltageclamping circuits each having a different clamping voltage, to which themost suitable voltage clamping circuit can be selected and assembled,for example using the method(s) described herein. In an exampleembodiment, the kit may further include any additional circuit elementas previously described herein providing the additional functionality tothe kit.

Variations may be made to some example embodiments, which may includecombinations and sub-combinations of any of the above. The variousembodiments presented above are merely examples and are in no way meantto limit the scope of this disclosure. Variations of the exampleembodiments described herein will be apparent to persons of ordinaryskill in the art, such variations being within the intended scope of thepresent disclosure. In particular, features from one or more of theabove-described embodiments may be selected to create alternativeembodiments comprised of a sub-combination of features which may not beexplicitly described above. In addition, features from one or more ofthe above-described embodiments may be selected and combined to createalternative embodiments comprised of a combination of features which maynot be explicitly described above. Features suitable for suchcombinations and sub-combinations would be readily apparent to personsskilled in the art upon review of the present disclosure as a whole. Thesubject matter described herein intends to cover and embrace allsuitable changes in technology.

Certain adaptations and modifications of the described embodiments canbe made. Therefore, the above discussed embodiments are considered to beillustrative and not restrictive.

What is claimed is:
 1. A method for selecting a clamping voltage for avoltage clamping circuit connected in parallel with a feedbackcompensator of a switching mode power supply, the method comprises:operating the switching mode power supply, without the voltage clampingcircuit, near a controllability and non-controllability boundary;identifying potential connection points for the voltage clampingcircuit, the potential connection points being in parallel with anoutput current path of the feedback compensator; calculating ormeasuring a maximum differential analog voltage at each of the potentialconnection points; and selecting the potential connection point and thevoltage clamping circuit having a minimally larger clamping voltage thanthe calculated or measured maximum differential analog voltage at eachof the potential connection points.
 2. The method of claim 1, wherein:the voltage clamping circuit provides transient overvoltage protection.3. The method of claim 1, wherein: the voltage clamping circuitcomprises at least one of a Zener diode, a shunt regulator, an activeZener device, a transient voltage suppression (TVS) diode, avoltage-dependent resistor (VDR), or an avalanche diode.
 4. The methodof claim 1, further comprising: placing the voltage clamping circuit inparallel with the selected connection points.
 5. The method of claim 1,the method further comprising varying at least one transient operatingcondition of the switching mode power supply.
 6. The method of claim 5,further comprising optimizing the voltage clamping circuit to minimize avoltage output settling time during the at least one transient operatingcondition.
 7. The method of claim 5, wherein: the at least one transientoperating condition comprises a heavy-to-light load transient operatingcondition, the method further comprising optimizing the voltage clampingcircuit to reduce feedback compensator wind-up and minimize an outputvoltage deviation during the heavy-to-light load transient operatingcondition.
 8. The method of claim 1, wherein the switching mode powersupply comprises: a converter; a voltage input for the converter; and avoltage output from the converter configured to be electrically coupledto a load, the feedback compensator controlling the converter inresponse to detecting the voltage output.
 9. The method of claim 8,wherein: the feedback compensator comprises an analog feedbackcompensator.
 10. The method of claim 9, further comprising: isolating,by the feedback compensator, the voltage output from a control signal ofthe convener.
 11. The method of claim 10, wherein: the feedbackcompensator is isolated using an opto-coupler.
 12. The method of claim8, wherein: the switching mode power supply comprises an anti-windupcircuit, the anti-windup circuit comprising the voltage clamping circuitand a current limiting circuit, wherein the anti-windup circuit preventsoccurrences or minimizes an absolute value of negative value controlsignals from the feedback compensator.
 13. The method of claim 12,wherein: the anti-windup circuit minimizes deviation of the voltageoutput during light-to-heavy transients.
 14. The method of claim 12,wherein: the current limiting circuit comprises at least one of afield-effect transistor, a resistor, a thermistor, or an active currentlimiter.
 15. The method of claim 8, further comprising: generating, bythe feedback compensator, a control signal for controlling theconverter.
 16. The method of claim 15, further comprising: generating,by the feedback compensator, the control signal using a comparisonbetween a detected voltage output and a reference voltage to reduce adeviation of the voltage output.
 17. The method of claim 16, wherein:the feedback compensator comprises a proportional-integral-derivativecontroller.
 18. The method of claim 15, wherein: the switching modepower supply further comprises a pulse width modulator; the methodfurther comprises controlling, using the control signal, the pulse widthmodulator; and providing, by the pulse width modulator, a switchinginput to the converter.
 19. The method of claim 15, further comprising:generating, by the feedback compensator, the control signal according toat least one of discontinuous-current modulation (DCM),continuous-current modulation (CCM), pulse-frequency modulation (PFM),or quasi-resonant frequency (QR) operation.